The author apologizes to those authors whose work could not be cited directly owing to space constraints. For stimulating discussions and critical reading of the manuscript the author is very grateful to S. Brabletz and M. Swierk. T.B. is supported by the DFG (no. BR 1399/6-1 and the SFB 850, B2), the Deutsche Krebshilfe (grant no. 109430), the Speman Graduate School of Biology and Medicine (SGBM) and the BIOSS Centre for Biological Signalling Studies.

Competing interests statement

The author declares no competing financial interests.

FURTHER INFORMATION
Thomas Brabletz’s homepage: http://www.uniklinik-freiburg. de/brabletzlab/live/index.html
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